Exploring, drilling, completing, and operating hydrocarbon and other wells are generally complicated, time consuming, and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on well access, monitoring and management throughout its productive life. Ready access to well information and intervention may play critical roles in maximizing the life of the well and total hydrocarbon recovery. As a result, downhole tools are frequently deployed within a given hydrocarbon well throughout its life. These tools may include logging tools to acquire data relative to well conditions as well as intervention tools to address downhole conditions.
The above noted downhole tools are generally delivered to a downhole location by way of a well access line. The line may be delivered by way of a winch at the surface of the oilfield which is directed to deploy the line into the well. The line itself may be a wireline cable or slickline for dropping the tool vertically into the well or a coiled tubing line for driving the tool downhole in a powered manner, such as for a highly deviated well. Regardless, once positioned to a desired downhole location, a well application may be employed by the tool at the end of the line. In conjunction with, or subsequent to, performing the downhole application, the winch may then be employed to withdraw the well access line and tool from the well.
Unfortunately, the well access line is susceptible to sustaining damage as it is positioned. That is, during the described advancing or withdrawing of the well access line, a load may be placed on the line which results in damage to the line. For example, the well access line may be a coiled tubing line as indicated. As such, a significant amount of power may be employed to drive the line through a tortuous or deviated section of the well. Thus, the coiled tubing line may be susceptible to sustaining buckling damage, for example, where it is directed to traverse a bend in the well that results in imparting a significant load on the end of the coiled tubing.
In another scenario, a well access line in the form of a wireline cable may sustain damage or even be broken during an attempt to withdraw from the well. For example, in many cases, the tool at the end of the line may become stuck in place downhole. This may be due to the presence of an unforeseen obstruction, unaccounted for restriction, differential sticking of the tool against the well wall, a malfunctioning tractor, or for a host of other reasons. Indeed, with the presence of increasingly deeper and more deviated wells, the likelihood of a downhole tool becoming stuck merely due to the depth and architecture of the well alone is increased. Regardless, once stuck downhole, an attempt to withdraw the wireline may lead to cold-flow damage and ultimately breaking of the line.
Once a wireline cable is broken as indicated above, potentially several thousand feet of line may be left in the well. To prevent this circumstance, a weakpoint is generally built into the logging head at the tool. Thus, the continued pull on the tool through the line may result in leaving only the downhole tool and part of the logging head behind. Unfortunately, this will generally require a subsequent fishing operation in order retrieve the tool from the well. Such a fishing operation may result in shutting down of hydrocarbon production for anywhere from a few hours to a few weeks. Ultimately, such a shut down may come at a cost of several hundred thousand to perhaps millions of dollars in lost production.
In an attempt to avoid such lost production time, efforts have been made at early detection of loads imparted on the well access line during downhole positioning thereof. So, for example, a detector may be placed at the winch to determine the amount of tension being imparted on the well access line, say a wireline cable, during its withdrawal as described above. Thus, as the wireline cable is withdrawn from the well, the load thereon may be monitored. As such, a signal may be sent to the winch to halt the withdrawal of the cable upon detection of a load approaching a predetermined amount thought to be damaging to the cable.
Unfortunately, early detection of load increase is generally insufficient to prevent damage to the line. For example, in the above scenario of withdrawing a wireline cable, withdrawal will generally take place at a very high speed, say between about 25,000 and 50,000 feet per hour. As a result, the natural delay between a detected spike in tension and the actual shutting down of the winch is such that damage to, or breaking of, the cable will generally result in spite of the early detection. Even though the natural delay between detection and effective shutting down of the winch may only be a few milliseconds, the spike in tension resulting in cable damage may be even shorter. Given the particular scenario of an obstructed tool or cable that is being withdrawn at high speed, the time between encountering a load due to an obstruction and damage to the line may be less than a millisecond. Furthermore, altering withdrawal to a low speed procedure in order to allow adequate time between load detection and shutting down of the winch would be substantially cost prohibitive.